Acyl taurinates and acyl isethionates, broadly classed as acyl aminoalkane sulfonates and acyloxyalkane sulfonates respectively, are known ingredients useful in synthetic detergent bars (syndet bars), shampoos, bubble baths, body washes, creams and lotions.
The reaction of acid chlorides of carboxylic acids with 2-amino- or 2-hydroxyalkanesulfonic acids and their alkali metal salts to yield anionic surfactants (for example, sodium N-acyltaurates and sodium acylisethionates, respectively) is well known as the Schotten-Baumann synthesis.
The Schotten-Baumann chemistry is very laborious and costly, requiring the handling of hazardous raw materials such as phosphorus trichloride and intermediates like acid chlorides as well as wastes like phosphorus acid. Large quantities of waste products are generated as a result of this chemistry. Also, the finished products contain significant amounts of sodium chloride as an undesirable by-product. The removal of the sodium chloride is possible, but expensive.
Sodium acyl aminoalkane sulfonate synthesis has been greatly improved by the direct amidation of sodium taurinate with fatty acids or by reacting a fatty amide with a sodium isethionate. This direct esterification route is cost-effective and these products are suitable for use in commercial toilet soap preparations.
The preparation of such sulfonates by direct amidation of an aminoalkane sulfonate with a fatty acid has presented difficulties because of the high temperature required to obtain suitable conversion. At temperatures required for direct acylation, usually in the range of 180.degree. to 250.degree. C., the molten reaction product rapidly degrades in color and loses activity. It has been found necessary to rapidly cool the reaction mass in order to obtain a final product.
PCT publication WO 95/18095 teaches preparing a taurinate by direct acylation, chilling the reaction mixture on a plate, redissolving the solid reaction mixture in lower alkanols or ketones under reflux followed by cooling to separate the insoluble product from the byproducts and solvent.
U.S. Pat. No. 2,697,872 teaches acylating a sodium N-methyl taurine with molten fatty acid anhydride in the absence of catalyst. The reaction generally is conducted at 1000 to 200.degree. F. (though higher temperatures are mentioned generically). At some temperature acetone is added and the mixture cooled to 60.degree. F. to isolate a purified product. It is noted that the acetone is added to the reaction mixture so that one would presume that the reaction mixture is not being quenched from an elevated temperature.
U.S. Pat. No. 3,429,136 teaches that in preparing acyl isethionates by direct esterification, the molten reaction mass can be cooled by injecting cold water directly into the molten crude reaction mixture to cool the mass by evaporative cooling below a temperature at which rapid discoloration would occur and this can be done without causing appreciable hydrolysis of the ester.
Since this crude reaction product ordinarily contains unreacted fatty acid, sulfonate or both, various methods have been proposed for purification. Generally these methods comprise forming liquid systems in which the impurities are soluble and the product is insoluble. Following cooling, the soluble impurities separated with the liquid by filtration means.
U.S. Pat. No. 4,515,721 teaches that excess fatty acid can be removed from an isethionate reaction mixture by quenching the hot crude fatty acid ester by immersion in a liquid in which the desired ester product is insoluble and the unreacted fatty acid soluble. The phases are separated to affect purification. In this patent the isethionate can be quenched in various products including lower chain length alcohols, fatty alcohols, fatty alcohol ethoxylates, polyethylene glycols, polyoxyalkylene derivatives of polyethylene glycol, fatty triglycerides, fatty esters and fatty amides. The preferable quenching liquid is isopropanol.
U.S. Pat. No. 4,612,132 describes a process for preparing an aqueous surfactant solution and gel of an acyloxyalkane sulfonate salt by combining the sulfonate salt with a water soluble polyol and water. This mixture is heated above the boiling point of water under super atmospheric pressure to form a reversible solid colloidal solution from which the product can then be recovered. See also, U.S. Pat. No. 4,696,767.
U.S. Pat. No. 5,415,810 discloses that blends of SCI and betaine (zwitterioncs) can be made in an aqueous system where the zwitterionic surfactant assists in the dissolution of the isethionate.
It is known to prepare blends of surfactants to accomplish various desired end results. Blends of isethionates and betaines, optionally with soap, are known for producing syndet bars (U.S. Pat. No. 5,372,751).
Presently, blends of taurinates and betaines are made by dissolving or slurrying the taurinate in a heated (400.degree. C.) aqueous betaine solution. This procedure requires the preparation of solid taurinate and the reheating of the betaine solution.
It is an object of the invention to prepare a high active content, substantially salt free acyl taurinate by a process which eliminates the steps of solidification and reslurrying. The present process is thereby more economical because the quenching operation is faster than the flaking operation insuring lower decomposition of product during manufacture.
It is also an object of the invention to prepare blends of taurinates with amphoteric and/or anionic surfactants, optionally with other ingredients and surfactants in a process which eliminates the need for solidifying and reslurrying the taurinate, reduces product decomposition, thereby making the product in a more economical manner.